With EWS, there are two aspects to syncing categories. SmarterMail and eM Client each support both parts.

First is the category list, which allows syncing the names and colors of the categories associated with your account. Using this, eM Client can retrieve your current category list from and push changes to SmarterMail.

The second part is which categories are assigned to any given item. This is done in EWS using a list of category names. These names are then matched against the list to identify the color associated with each category. This makes it possible for a client such as eM Client to assign a category to an item that is not on the list. SmarterMail handles that scenario by adding the category to the list for your account, but without assigning a color.

The behavior you described probably happened because eM Client has multiple category lists. You can see this most clearly in their Tags window^†. In the Tags window, there is a dropdown just to the right of the save button. This dropdown should have a Local Tags option, as well as an option for each EWS account you have configured. Only tags that are listed when you select your account are are fully synced to the server. If you assign tags that are in the Local Tags list, it will sync to SmarterMail as a colorless category, unless you already have a category that has the same name.

Andrew, 

thanks for the tip.

 

Tags can also be added directly from emClient to the SM account via the tags in the menu.

It's just a bit more complicated than in Outlook and requires some explanation, but that's no problem ;) 

That definitely helped me.

Regards

Oliver